Terminal blocks are commonly used in telephone distribution lines. For example, a telephone cable will lead from the telephone company system to a terminal block. The terminal block has a base with a number of connection stations, for example 10 to 15. Each station has a separate electrical connector which will connect one twisted-pair of wires in the incoming telephone cable to one of the drop lines which lead to one of the individual telephone sets. The wires from the incoming telephone cable are prewired into the stations of the base. Each station has two holes for insertion of the two wires from one of the drop lines. Normally, the station will have an installation displacement terminal (referred to as "IDC) registering with each of the holes. An IDC terminal allows the operator to insert the ends of the drop line into the holes in the station without stripping the insulation from the ends. The IDC terminal has a slit with two sharp edges that are biased toward one another. The wires are pressed through the slit toward the base, making contact without the need for stripping.
When installing distribution terminals, it is not uncommon for the telephone company cable to have more capacity initially than will be required by individual drop lines. For example, the incoming cable may have a capacity for 15 sets of drop lines, but only eight will be initially used, although it is possible in the future that the rest will be needed. The company installing the distribution terminal may install a terminal block that has 15 separate stations to match the full capacity of the cable even though only eight are being used. Later, when the others are going to be used, the drop lines can simply be inserted into the stations. However, a larger terminal block than initially needed is more expensive. If the company elects to install a smaller terminal block, it may find that it later has to replace the smaller terminal block with a larger one.